Hydraulic actuator

ABSTRACT

A hydraulic actuator for producing translational movement over a long distance having two jack cylinders with pistons mounted for reciprocal movement and connected to a worm wheel through a worm gear. When a piston is driving, the worm gear acts as a rack to turn the worm wheel and when a piston is being returned to its starting position the worm gear rotates. Means are provided to alternately switch from one cylinder to the other.

O Umted States Patent 1 3,703,851

Ifield et al. [4 1 Nov. 28, 1972 [54] HYDRAULIC ACTUATOR 2,808,03310/1957 Geier et al. ..92/31 X 72 Inventors: Richard Jmeph Ifield;2,970,574 2/1961 Geyer 33 X Robert meld, both of Carters Road 3,000,3579/ 1961 Geyer ..92/33 X Dural Australia 3,179,0l5 4/1965 Kurt ..92/ 136X [22] F d Dec 23 1970 3,187,592 6/1965 Geyer ..92/33 X 211 App] 1 0 9Primary Examiner-Martin P. Schwadron Assistant Examiner-Ronald H.Lazarus At gn pplication r ority Data tomey-Stevens, Davis, Miller &Mosher Jan. 6, 1970 Australia ..0018 ABSTRACT A hydraulic actuator forproducing translational }LtS.CCI )3 movement over a long distance havingtwo jack cylin i 17 1/36. ders with pistons mounted for reciprocalmovement 9 and connected to a worm wheel through a worm gear. When apiston is driving, the worm gear acts as a rack to turn the worm wheeland when a piston is being [56] References Cited returned to itsstarting position the worm gear rotates. UNITED STATES PATENTS Means areprovided to alternately switch from one 2 979 034 4/1961 Gey 92/33 X'cylinder to the other' er 3,414,693 12/1968 Watson et al ..92/5 X 5Claim, 5 Drawing Figures PATENTED 28 I97? 3 7 O3 8 51 SHEET 2 OF 4PAIENTED nuv 28 m2 SNEEI 3 0F 4 HYDRAULIC ACTUATOR This inventionrelates to actuators for the movement of substantial loads throughsubstantial distances.

Actuators of the kind to which the invention relates may be used, forexample, for the lifting or hauling of heavy loads, the straining ofpre-stressing cables in concrete structures, the rotation of machineelements against the effects of heavy restraining torques and the like.

Many relatively simple actuators are known for the shifting of heavyloads through short distances, for example, mechanical or hydraulicjacks, but prior known actuators for producing translational motion overa long distance or continuous rotary motion have been elaborate andtherefore expensive.

An object of the present is to provide an actuator of the kind underdiscussion which is relatively simple in construction and,,therefore,inexpensive to manufacture.

The invention achieves that object by the provision of two hydraulicjack cylinders which work in concert and which are effective to move aload in increments with one jack cylinder taking over from the other atthe end of each increment to provide substantially continuous motion.

Thus, the invention consists in an actuator comprising a body structuredefining two jack cylinders and ducts for the supply of pressurizedhydraulic fluid to, and exhaust of fluid from, said jack cylinders, twopistons disposed one in each cylinder, changeover valve meanscontrolling the admission and exhaust of fluid to and from saidcylinders in a manner causing said pistons to reciprocate through powerand return strokes with the power stroke of one piston alternating withthat of the other and with substantially no time delay betweensuccessive power strokes, and power transmission means whichdrive-connect each said piston to a load to be moved during the pistonspower stroke but release each piston from the load during the piston sreturn stroke.

According to the invention the power transmission means comprises ahelicoidal elements, such as a nut or a worm which engages a co-actingloaded element, such as a threaded shaft or a worm-wheel, together withmeans to rotate the helicoidal element during the return stroke of itsassociated piston to permit the helicoidal element to movetranslationally relative to the loaded element. On the other hand,during the power stroke of its associated piston the helicoidal elementis not rotated and, thus, translational movement imparted to it by itsassociated piston causes the required motion of the loaded element,which is thereby transmitted to the load to be moved.

The invention is applicable to the rotation of a load in eitherdirection in a controlled and irreversible manner. For example, it maybe incorporated in the drive for slewing a large crane, turning a winchdrum or similar application. It is also applicable to providing acontinuous linear motion on a long shaft.

Certain embodiments of the invention will now be described withreference to the accompanying drawings in which:

F IG. 1 shows, in front elevation and partly in section, an actuatoradapted for rotary motion,

FIG. 2 shows, in end elevation and partly in section, a view along theline 2-2 of FIG. 1,

FIG. 3 shows, in front elevation and partly in section, an actuatoradapted for translational motion, and

FIG. 4 shows, in elevation, a view along the line 4-4 of FIG. 3.

Upon referring to FIGS. 1 and 2 of the drawings it will be seen that thedrive transmission means include a loaded element that is to say anelement which carries or is connected to the load to be moved in theform of a worm-wheel 5 mounted for rotation about an axis 6 which isfixed relatively to the body structure 7 of the actuator.

The body structure 7 enclosing the worm wheel contains pairs of jackcylinders such as 8 and 9 with closed ends and having their axestangential to and in the same plane as the worm wheel 5. For continuousrotation of the worm wheel at steady torque there must be at least twopairs of such jack cylinders, but any greater number of pairs may beemployed to increase the driving torque for a given maximum worm toothloading, the number being limited only by the available peripheral spacearound the worm wheel. In order to simplify the description, it will beassumed that only two pairs of cylinders are employed.

A respective pair of jack pistons 10 and l 1 is slidably mounted in jackcylinders 8 and 9. The jack pistons have a sealed piston head at eachend sliding in the jack cylinders. The center portion of the jackpistons is of helicoidal form as a worm l2 engaging the teeth of theworm wheel 5. Preferably the worm has a single start and isirreversible. Each pair of jack pistons has a slidable drive connectionsuch as 13 passing through a seal such as 14 in the end wall of cylinder9, to provide means for rotating the worm 12 on its unloaded returnstroke.

Purely for descriptive purposes, where it is necessary to distinguishbetween them, the pair of jack cylinders 8 and 9 and its associatedjack, drive shaft and other associated components will be referred to asthe first and the other pair of jack cylinders and its associated jack,drive shaft and other associated components enclosed within the housing15 will be referred to as the second components as named.

The body structure 7 also defines ducts for the supply of pressurizedfluid to and the exhaust of fluid from the closed ends of the cylinders.

One end of the second pair of cylinders has a duct B. The adjacent endof the first pair of cylinders has a duct C. The opposite ends of thepairs of cylinders are adjacent to one another and are interconnectedwith a common duct A.

For one direction of drive, duct B is at high pressure continuously andduct C is at low pressure continuously. These pressures are reversed forthe opposite direction of drive.

Duct A is connected to any suitable automatic valve (see FIG. 5),oscillating to pressurize and exhaust the duct. The automatic valve maybe an electric solenoid operated valve responsive to the triggering ofthe double acting micro switch 16 operated by the lost motion stop rod17 at each end of the stroke of piston 10, or it may be any other formof snap action valve, triggered at each end of the piston stroke. Themicro switches or other triggering devices are required at only one pairof .pistons, in this case the first pair. Because the automatic valve istriggered at each end of the stroke of the first pair of pistons someexcess movement may be allowed at these pistons to ensure triggering ofthe valve before the piston reaches the limits of its movements.

It will be assumed that clockwise rotation of the worm wheel is desiredand this is provided when duct B is at high pressure and duct C is atlow pressure.

When duct A is exhausted to low pressure through the automatic valve,the pressure at duct B thrusts the second piston axially to rotate theworm wheel clockwise, the worm teeth acting as rack teeth during thismotion. During this operation there is no pressure difference at thefirst pair of pistons.

When duct A is pressurized through the automatic valve, there is nopressure difference at the second pair of pistons and the first pistonis thrust axially to rotate the worm wheel clockwise, the worm teethacting as rack teeth during this motion.

During the period when one pair of pistons is thrusting axially torotate the worm wheel, the other pair of pistons must return to theirstarting point ready for the next power stroke. This is achieved byrotating the pistons with their associated worm so that they screw backto theirstarting point. There is no loading on the pistons during theirreturn stroke so that they may be rotated with a relatively small powersupply. This rotation may be provided by small electric or hydraulicmotors, such as the hydraulic motor 18, but the pistons must be returnedfully before the other pair of pistons have reached the end of theirpower stroke, in order to ensure continuous operation.

The direction of rotation of the motor or motors, which rotate thepistons on their return strokes, must be reversed for the oppositedirection of rotation of the worm wheel.

Because the switching mechanism for the automatic valve is associatedonly with the first pair of pistons, this pair of pistons will alwaysoperate over the full stroke. For a given worm wheel speed, the strokeof the second pair of pistons will depend on the speed of the returnstroke of the first pair of pistons, which must trigger the automaticvalve before the second pair of pistons reach the limit of the powerstroke.

Instead of employing a separate motor to rotate each pair of pistons onthe return stroke, a single motor (not shown) may drive the two pairs ofpistons through differential gearing (not shown).

Because the worm drive is irreversible, the worm wheel is held againstrotation when the power is shut off.

If it is desired to hold the worm wheel without backlash, one of the twopiston rotating motors may be reversed, without reversing the other, orthe automatic valve may be prevented from operating. In either case thetwo pairs of pistons would then move to their adjacent stops, whichprevents movement in either direction of rotation of the worm wheel.

There is a variety of different arrangements of pumps and valves whichare suitable for the power supply and these do not form part of theinvention. One suitable arrangement is shown diagrammatically at FIG. 5to clarify the operation of the actuator, as described with reference toFIG. 1. The connections to the actuator ducts are identified in FIG. 5by similar letters. FIG. 5 shows a separate pump to power the smallmotors 18 shown on FIG. 1, these have a common inlet duct and a commondelivery duct, which are reversible for the opposite direction ofrotation and are identified by the letters D and E.

FIG. 5 shows diagrammatically a main variable displacement power supplypump 33, the output of which determines the rotational speed of theactuator. A small fixed displacement pump 34 is shown to rotate themotors 18 during the unloaded return strokes of the pistons; the outputof this pump must be adequate to return the pistons fully on theirreturn strokes for the highest actuator speed and the excess flow fromthe pump is discharged through the relief valve 35. A relief valve 36 isalso shown to prevent overload at the .main pump 33. Two manuallyoperated reversing valves 37 and 38 are shown to reverse the high andlow pressures to ducts B and C and to reverse the direction of rotationof the small motors 18, FIG. 1 when it is required to reverse thedirection of rotation of the actuator.

The automatic valve previously referred to is shown at 39 as a solenoidoperated valve, the previously being energized in response to themovements of the rpeviously described microswitch 16, at each end of thestroke of the worm 12. The movements of this automatic valve cause theduct A to alternate between the pressure supply from the pump 33 and thedischarge to the reservoir 40.

According to a second embodiment of the invention a linear actuator isprovided, as shown in FIGS. 3 and 4.

In this instance, the two jack pistons may be in the form of nuts 19 and20 on a threaded shaft 21, being the helicoidal member to which the loadto be moved is connected.

The body structure 22 surrounds the threaded shaft which extendsco-axially through the two jack cylinders 23 and 24. The jack cylindersmay be opposite end portions of a single cylindrical cavity and bothjack pistons may have respective axially extending skirts 25 and 26thereon which project through sealing glands at the outer ends of thecylindrical cavity. Furthermore, the jack pistons may have inwardlydirect skirts thereon, slidable telescopically within the housing 22,and each having respective annular fluid seals 28 and 29 to preventleakage of fluid from the cylinders to the screw-threaded shaft.

Each jack piston may have a respective spur gear 30 and 31 fixed to itsoutwardly projecting skirt outside the jack cylinder space and said spurgears may mesh respectively with pinions such as 32 driven by returnmotors as described in the first embodiment of the invention.

As in the first embodiment, duct A leads to the space between the twopistons, duct B leads to one closed end of the cylinder and Duet C leadsto the other closed end of the cylinder.

The double acting micro switch 27 or other triggering mechanism (seeFIG. 5) for the automatic valve may be operated at the ends of thestrokes of the first piston as previously described in the first exampleof the invention.

As described in the first embodiment the two return motors may bereplaced by a single motor, rotating the two pistons on their returnstrokes, through differential gearing.

The operation is similar to that described for the first embodiment.Duct A is at high pressure when the pistons are closest together and atlow pressure when the pistons are furthest apart. When duct A is at highpressure, the opposite face of the first piston is at low pressure andthe piston thrusts the screwed shaft axially; the opposite face of thesecond piston is at high pressure, so there is no pressure differenceand the piston is rotated, screwing along the shaft against the stop,until the first piston triggers the switch. Duct A now changes to lowpressure, causing the second piston to thrust on the shaft and allowingthe first piston to rotate, screwing along the shaft until if triggersthe switch to repeat the cycle of operation.

Where several rotary actuators, as described in the first embodiment, orseveral linear actuators as described in the second embodiment, arerequired to operate in parallel and in phase with one another, it ispreferred to employ solenoid operated automatic valves, with microswitches triggered by the movements of both jack pistons. in this casethe micro switches of each actuator are connected in series pairs andthese pairs for all actuators are connected in series, to operate asingle automatic valve, or any number of automatic valves. This ensuresthat all jack pistons operate over their full stroke and that theseparate actuators remain in phase with one another, regardless ofloading differences, within the limits of one piston stroke.

We claim:

1. A hydraulic actuator comprising a body structure defining two jackcylinders and ducts for the supply of pressurized hydraulic fluid to,and exhaust of fluid from, said jack cylinders, tow pistons disposed onein each cylinder, each having a helicoidal portion in the form of ascrew thread co-acting with a mating portion of an actuator, changeovervalve means controlling the admission and exhaust of fluid to and fromsaid cylinders in a manner causing said pistons to reciprocate throughpower and return strokes with the power stroke of one piston alternatingwith that of the other and with substantially no time delay betweensuccessive power strokes, and means to rotate a selective piston toenable it to move back to its staring position while the other pistondrives said mating portion.

2. An actuator as claimed in claim 1, wherein said jack pistons have adrive connection passing through a seal, said drive connection beingrotatable during the return unloaded stroke of said pistons.

3. An actuator as claimed in claim 1, wherein a plurality of saidcylinders is disposed in the available peripheral space around saidmating portion.

4. An actuator as claimed in claim 5, wherein an automatic valveresponsive to triggering by path limit detecting means at each end ofthe stroke of one of said pistons is adapted to pressurize and exhaustsaid ducts successively with an oscillatory action, whereby no pressuredifference exists at one pair of said pistons while one of another pairof said pistons is thrust axially to rotate said mating portion, or tomove a linear actuator axially relative to a screwed shaft.

5. A hydraulic actuator comprising:

a. a body structure defining two jack cylinders and ducts for the supplyand exhaust of pressurized fluid to and from said cylinders, b. twopistons disposed one in each cylinder, each

1. A hydraulic actuator comprising a body structure defining two jackcylinders and ducts for the supply of pressurized hydraulic fluid to,and exhaust of fluid from, said jack cylinders, tow pistons disposed onein each cylinder, each having a helicoidal portion in the form of ascrew thread co-acting with a mAting portion of an actuator, changeovervalve means controlling the admission and exhaust of fluid to and fromsaid cylinders in a manner causing said pistons to reciprocate throughpower and return strokes with the power stroke of one piston alternatingwith that of the other and with substantially no time delay betweensuccessive power strokes, and means to rotate a selective piston toenable it to move back to its staring position while the other pistondrives said mating portion.
 2. An actuator as claimed in claim 1,wherein said jack pistons have a drive connection passing through aseal, said drive connection being rotatable during the return unloadedstroke of said pistons.
 3. An actuator as claimed in claim 1, wherein aplurality of said cylinders is disposed in the available peripheralspace around said mating portion.
 4. An actuator as claimed in claim 5,wherein an automatic valve responsive to triggering by path limitdetecting means at each end of the stroke of one of said pistons isadapted to pressurize and exhaust said ducts successively with anoscillatory action, whereby no pressure difference exists at one pair ofsaid pistons while one of another pair of said pistons is thrust axiallyto rotate said mating portion, or to move a linear actuator axiallyrelative to a screwed shaft.
 5. A hydraulic actuator comprising: a. abody structure defining two jack cylinders and ducts for the supply andexhaust of pressurized fluid to and from said cylinders, b. two pistonsdisposed one in each cylinder, each having a screw threaded portion, c.power transmission means threadingly engaging the screw threaded portionof each piston, d. means to rotate a selective piston to enable it tomove back to its starting position while the other piston drives saidpower transmission means, and e. changeover valve means controlling theadmission and exhaust of fluid to and from said cylinders in a mannercausing said pistons to reciprocate through power and return strokeswith the power stroke of one piston alternating with that of the otherand with substantially no time delay between successive power strokes.